1. Field of the Invention
The invention relates to ultrasonic surgical clamping and cutting instruments. More particularly, the invention relates to an improved power limiting mechanism for ultrasonic surgical cutting and clamping instruments.
2. Description of the Prior Art
Ultrasonic instruments are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments are advantageous because they may be used to cut and/or coagulate organic tissue using energy in the form of mechanical vibrations transmitted to a surgical end-effector at ultrasonic frequencies.
Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels and using a suitable end-effector, may be used to cut and/or dissect tissue. Ultrasonic instruments utilizing solid core technology are particularly advantageous, because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer through the waveguide to the surgical end-effector. Such instruments are particularly suited for use in minimally invasive procedures, such as, endoscopic or laparoscopic procedures, where the end-effector is passed through a trocar to reach the surgical site.
Ultrasonic vibration is induced in the surgical end-effector by, for example, an electrically excited transducer that may be constructed of one or more piezoelectric or magneto-resistive elements in the instrument handpiece. Vibrations generated by the transducer are transmitted to the surgical end-effector via an ultrasonic waveguide extending from the transducer section to the surgical end-effector.
Many such ultrasonic surgical instruments are known within the prior art. However, they are highly responsive to the pressure applied by the surgeon. In particular, as the surgeon applies greater pressure, the vibration characteristics of the ultrasonic instrument are altered. In fact, in situations where a surgeon exceeds a predetermined pressure level, the power delivered to the tissue may be too high. This may result in undesired tissue effects, such as poor hemostasis of transacted vessels. Furthermore, it is possible that the surgical instrument might not be equipped to handle the material stress requirements for producing the vibration levels at the high pressure levels, thus resulting in undesirable operation of the instrument. Attempts have been made to remedy problems associated with the application of different pressures, for example, by the inclusion of springs within the actuation assembly to mechanically attempt to control applied pressure. However, these attempts have been met with only limited success.
As such, a device is needed wherein a constant power profile is achieved despite personal preferences in the force applied by the surgeon. The present invention provides such a device.